The two sides disagree on the price and size of the stake and how much management control would be handed to Son, said two people, who like the others asked for anonymity disclosing confidential information. Issues within SoftBank, such as the pending merger of its Sprint Corp. business with T-Mobile US Inc., and the initial public offering of SoftBank’s mobile unit, have also shifted Son’s focus, the people said.

While the talks cooled in recent weeks, they could still be revived, the people said. Officials for Swiss Re and SoftBank declined to comment.

A deal would help Son, who is reshaping Japanese mobile-phone carrier SoftBank into a technology investor, follow other business titans such as Warren Buffett in seeking to profit from the cash flows provided by reinsurance.

But Swiss Re executives have pushed back against expectations that the company’s assets could be used to buttress Son’s investment projects, saying talks were limited to a stake of 10 percent or less. Initially, people familiar with the matter said SoftBank was seeking to buy as much as a third.

“If you have a small stake, you cannot influence the capital position, the assets,” Swiss Re Chief Executive Officer Christian Mumenthaler said on a conference call last month. “I feel there is a lot of paranoia about it.”

Adding to challenges for the deal, Chief Financial Officer John Dacey told investors it was “highly unlikely” that the company would sell treasury shares as part of the deal. Swiss Re’s reluctance to issue new shares means Softbank must buy its stake on the open market at a price which has risen more than 4 percent since the talks were first announced, another person said.

Mumenthaler has said that the talks were initiated by SoftBank. UBS Group AG is advising Softbank, while Credit Suisse Group AG is advising Swiss Re.

Son has a net worth of about $14 billion and is Japan’s third-richest person, according to the Bloomberg Billionaires Index.